This invention relates to an exhaust gas recirculating valve control method for internal combustion engines, and more particularly to a method of this kind, which is adapted to prevent making a wrong diagnosis upon detecting abnormality in an exhaust gas recurculating valve control system as well as to ensure required durability of the exhaust gas recirculating valve control system.
A method is generally known, which is adapted to recirculate part of exhaust gases from the exhaust passage of an internal combustion engine to the intake air passage of the engine to thereby reduce nitrogen oxide which is one of the detrimental gases generated from the engine. Also, in order to determine an appropriate exhaust gas recirculating quantity in response to operating conditions of the engine, an exhaust gas recirculating valve control method has been used, which is adapted to detect actual valve opening of an exhaust gas recirculating valve arranged across an exhaust gas recirculating passageway, and control the actual valve opening value so that it approaches a desired valve opening value calculated in response to the operating conditions of the engine.
In such an exhaust gas recirculating quantity control method as stated above, when abnormality occurs in valve opening detecting means including a valve opening detecting sensor for detecting the valve opening of the exhaust gas recirculating valve due to disconnection in the wiring, etc., it is impossible to accurately control the exhaust gas recirculating quantity, which can even cause the phenomenon that exhaust gas recirculation is effected when it is unnecessary, depending upon operating conditions of the engine, resulting in heavy deterioration of the engine. Therefore, it has been proposed by Japanese Provisional Patent Publication (Kokai) No. 55-123345, to give an alarm when it is detected that the ratio or the difference between the actual valve opening value detected by the valve opening detecting sensor and the desired valve opening value falls outside an allowable range.
However, if the desired valve opening value calculated in response to operating conditions of the engine exceeds of a maximum possible valve opening of the exhaust gas recirculating valve, i.e., a valve opening beyond which the exhaust gas recirculating valve cannot be operated, the difference between the actual valve opening value and the desired valve opening value will not be reduced even if a control signal is issued for operating the exhaust gas recirculating valve to the desired valve opening value. As a consequence, it can be wrongly judged that the exhaust gas recirculating valve has developed an abnormality.
Further, in an exhaust gas recirculating valve control system in which the exhaust gas recirculating valve is driven by pressure respsonsive type valve actuator means which is responsive to hydraulic pressure for instance, if the desired valve opening value is set to a value beyond the maximum possible valve opening of the exhaust gas recirculating valve, the hydraulic pressure is set to such a value as to cause a larger differential pressure to act upon the valve actuator means so as to open the exhaust gas recirculating valve to an opening degree closer to the set desired valve opening value. However, the larger the differential pressure acting upon the valve actuator means, the more easily the hydraulic pressure can leak from the valve actuator means. Also, the valve actuator means thus acted upon by the large differential pressure can deteriorate in durability such as the effective life. On the contrary, if the valve actuator means, etc. are designed so as to be free from such leakage of the hydraulic pressure as well as to ensure required durability of the valve actuator means, etc. it will necessarily result in increased sizes and weights of the valve actuator means, etc. as well as increased manufacturing costs thereof.